Importance

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Abstract

The cryptographic system is comprised of two stations A and B in which a respective string S.sub.A and S.sub.B of digits is stored. In station A an error-control information string C is generated from string S.sub.A and transmitted to station B over an error-free public channel CH1. In station B a particular string D and a decision bit F are generated. String D maximizes a predetermined reliability function of a string combination (S.sub.B, C, D). Decision bit F is assigned the value 1 if and only if a maximum value taken on by the reliability function is greater than a predetermined threshold. Decision bit F is transmitted to station A over an error-free public channel CH2. In both stations A and B, the respective strings S.sub.A and S.sub.B are tagged as accepted when said decision bit F has the value 1. The above sequence is repeated, resulting in a plurality of tagged strings which are concatenated at stations A and B to result in a random cipher key shared by the stations A and B. The predetermined reliability function can be defined as a conditional probability P (S.sub.A =D/S.sub.B =S.sub.B, C=C) that a random variable S.sub.A corresponding to string S.sub.A is equal to string D, given the conditions that a random variable S.sub.B corresponding to string S.sub.B is equal to that latter string S.sub.B and a random variable C corresponding to the error-control information string C is equal to that latter string C.

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First Claim